Wide area trunking communication systems are known to comprise a plurality of communication units, a plurality of sites, a limited number of communication resources, and a communication resource allocator. Typically, the plurality of communication units are arranged into communication groups. A wide area trunking communication system allows a communication unit to communicate with its communication group from any site in the system.
A difficulty arises in a wide area trunked communication system, when a member of the communication group is in a site that does not have an available resource. In such situations, one prior art solution was to wait until all sites, currently supporting some portion of the group population, had an available resource and then place the call. This allowed the group call to be fully processed, however, there was the potential of extended wait time while awaiting communication resource availability at all the sites for the call. Another approach was to allow the requesting communication unit to override the busy condition such that the resource allocator need only address resource availability at some pre-determined, select set of sites, instead of all the sites currently supporting some portion of the group population. This has the potential to reduce wait times over that experienced by awaiting resource availability at all the populated sites for this group. See Felderman U.S. Pat. No. 5,101,502 for a further discussion of busy override in a wide area trunked communication system which is incorporated herein.
In many communications, the requesting communication unit does not need to talk to the whole group, rather only a portion of it. Thus, the methods for communicating with a communication group described above waste communication resources and delay access time for small audience calls. Therefore, a need exists for a method that allows a group call to be directed to only a portion of the communication group.